Drum-boiler control system employing shrink and swell effect remission in thermal power plants

This paper develops a control system for a drum-boiler unit, which employs a three element cascade control (water level, steam flow, feed-water) versus a single element control for the water level loop, in order to attenuate the non-minimum phase shrink-and-swell effect. The overall control structure includes a heat flux control loop for throttle pressure stabilization. Gain scheduling technique is added to improve system responses at various operating points. The process is built around the Åström-Bell non-linear complex drum-boiler model fitted for a real 16 MW thermal power plant. The model is extended with actuators, super-heater and turbine dynamics. The implementation is carried out in Labview, employing a graphical user interface (GUI) for friendly man machine interaction with selection of manual/automatic mode. The simulation results are focused on manual/automatic control operation with satisfactory response behaviors.